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What to Know Before You Buy an Oral Basal Body Thermometer

Taking your basal body temperature daily with a basal body thermometer is one way of narrowing down the window of ovulation. People use basal body temperature to track ovulation for conceiving, avoiding pregnancy, or tracking their health. There are several factors to consider when buying a basal body thermometer, but it is important to first understand why basal body temperature can be used to track ovulation. 

what to know before buying a basal body thermometer

After ovulation, our core resting body temperature, or our basal body temperature, rises by a very small amount. This is due to the presence of progesterone acting on our body systems to warm us up slightly. Ovulation is tracked through basal body temperature retrospectively, meaning, we only know it’s happened after the fact. Using both cervical mucus and basal body temperature can narrow down the fertile window even more, and other additional markers of fertility can be helpful in identifying the approximate time of ovulation. 

Taking your basal body temperature every day gives you an idea of your pre-ovulatory range of temperatures as well as your post-ovulatory range of temperatures. You won’t have the same exact temperature every day, but your temperatures will be within a certain range depending on where you are in your cycle.

Your basal body temperature rises prior to your temperature shift, a very slight rise in temperature that is as little as 0.05C/0.1F. Identifying this shift as well as the range in pre-ovulatory and post-ovulatory temperatures is how you can know if ovulation has taken place. It’s important to note that symptothermal methods of fertility awareness rely on both cervical mucus and basal body temperature. Relying on temperature alone is not sufficient for avoiding pregnancy with symptothermal fertility awareness methods.

There are several different fertility awareness based methods (FABMs). If you are wanting to buy a basal body thermometer you will want to educate yourself in a symptothermal fertility awareness based method (basal body temperature and cervical mucus). You can either teach yourself by reading a book like Taking Charge of Your Fertility, or you can work with an instructor in your method of choice. It’s important to note that if you are using fertility awareness to avoid pregnancy, effectiveness is improved if you work with an instructor.  

When you look for a basal body thermometer, ensure that it goes to two decimal places and it is indeed a basal body thermometer, not a fever thermometer. A fever thermometer is not sensitive enough to pick up the slight increase in temperature following ovulation. You can take your temperature orally or vaginally, but just make sure you stick with the same one for your whole cycle. To get an accurate reading using a regular basal body thermometer (not a Tempdrop), you need at least three hours of consecutive sleep, and you take your temperature at the same time each morning before getting out of bed. 

Some thermometers have special features, such as remembering your past temperatures, having a backlight, or connecting to your phone via bluetooth. To start with charting your cycles you don’t need a fancy thermometer, but some of these features make it easier to stick with the habit of taking your temperature (which is a plus!). There may also be certain scenarios that make it more difficult to take your temperature after three consecutive hours of sleep or at the same time.

The Tempdrop wearable thermometer is great for things like working night shifts, irregular schedules or postpartum by allowing you to sleep in and not wake up to take your temperature, which is a huge bonus! If you are charting to avoid pregnancy, be wary of thermometers that take your wrist temperature - these are not accurate enough to be used for avoiding pregnancy. 

When charting your basal body temperature it is advised to round your temperatures. This makes your charts easier to read. In Celsius, you round scientifically to the nearest .00 or 0.05, and in Fahrenheit you round scientifically or drop the last digit.

rounding temperatures from your basal body thermometer

Find something to record your basal body temperature in, whether it is a paper chart or in an app. Apps that I recommend allow you to chart both cervical mucus and basal body temperature, and are like paper charts on your phone. These are Kindara, Ovuview (Android), Fertility Friend and the forthcoming Read Your Body app.

And that’s it! Are you inspired to start taking your basal body temperature? You can start any day if you are cycling naturally. Remember that day 1 is the first day of full bleeding. Do you have questions about basal body temperature? Pop them in the comments!

Nathalie Daudet at Fertility Awareness Project

Nathalie Daudet is a social worker and FEMM instructor based in Winnipeg, Canada. She discovered fertility awareness after searching high and low for a non-hormonal method of birth control. After learning the magic of fertility awareness and the gift of body literacy, she decided to pursue formal fertility awareness training and share the knowledge of fertility awareness with women looking for a natural birth control option. Fertility Awareness Project is the hub for Nathalie’s FEMM classes in both group and individual formats, online and in person in Winnipeg. If you love this post and would like to thank Nathalie, shop Tempdrop with Nathalie's unique referral link

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